2.6 Modularity assessment methods
In the evaluation of modularity of contiguous skull landmarks based on
the hypothesis that covariance between true modules (embryologic
relations) should be lower than for other developmentally unrelated
parts, the extent of such covariation is expressed in terms of the RV
coefficients; RV coefficient (Relative variance); as explained by
Escoufier (1973); is a similarity coefficient between positive
semi-definite matrices or simply a multivariate generalization of the
squared Pearson correlation coefficient (values between 0 and 1), it
measures two sets of points that may be represented in a matrix; the
closer to 1 the RV becomes, the more similar the two matrices. The
eleven dorsal view landmarks were divided into two subsets of equal
number of landmarks; only landmarks forming contiguous configurations
were allowed to run with full enumerations of partitions using MorphoJ
software vers. 2.0 (Rholf, 2015) (MorphoJ is available freely under the
Apache Licence, Version 2.0, from the web site
http://www.flywings.org.uk/MorphoJ_page.htm)